Groove type solar vacuum heat collecting tube with rotating inner core structure

Abstract

This invention provides a trough-type solar vacuum collector tube with a rotating inner core structure, comprising a glass outer tube, a metal heat-absorbing inner tube, a hollow rotating inner core tube, an end sealing assembly, a bent-tube inlet assembly, and an active drive and speed control system. The hollow rotating inner core tube and the metal heat-absorbing inner tube are arranged coaxially to form an annular flow channel. The heat transfer medium enters the annular flow channel through the bent-tube inlet assembly and flows axially. The rotating inner core tube rotates under the drive of the active drive and speed control system, causing the heat transfer medium to form a rotating shear flow. The end sealing assembly at the drive end has an annular medium inlet, allowing the heat transfer medium to enter the annular flow channel uniformly along the circumference. The active drive and speed control system adjusts the speed in real time according to the solar radiation intensity and the circumferential temperature difference. This invention can effectively homogenize the circumferential temperature distribution of the metal heat-absorbing inner tube, reduce the circumferential temperature difference, and reduce thermal stress, making it suitable for medium- and low-temperature industrial heating and high-temperature solar thermal power generation scenarios.

Description

Technical Field

[0001] This invention belongs to the fields of solar thermal utilization, enhanced heat transfer and fluid mechanics, and particularly relates to a trough-type solar vacuum collector tube with a rotating inner core structure. Background Technology

[0002] Solar energy, as the most widely distributed, abundant, and clean renewable energy source on Earth, has become one of the core supporting energy sources for global energy transition and achieving the "dual carbon" goal. Parabolic trough solar collectors are one of the most widely used heat collection forms in solar thermal power generation and industrial heating, and also one of the most mature technologies for medium- and high-temperature solar thermal applications. They also have strong promotional value in industrial steam, chemical heating, and food processing heat supply, attracting widespread attention. The vacuum collector tube is the core component of the parabolic trough solar collector system. Its structure typically consists of a coaxially arranged transparent glass outer tube, a metal heat-absorbing inner tube, and a high-vacuum insulation layer between them. During operation, the parabolic trough concentrator mirror focuses parallel sunlight onto the outer wall of the metal heat-absorbing inner tube. The metal heat-absorbing inner tube converts solar radiation energy into heat energy through the selective absorption coating on its outer wall, and then transfers the heat to the heat transfer medium flowing inside the tube through the tube wall, ultimately achieving a highly efficient conversion of solar energy into heat energy.

[0003] However, existing trough-type solar vacuum collector tubes have at least the following three technical defects:

[0004] 1) The uneven circumferential heating of the metal absorbing inner tube, resulting in severe thermal stress damage, is the core cause of collector tube failure. Due to the concentrating characteristics of the parabolic trough, reflected solar radiation is highly concentrated on the semicircular arc of the metal absorbing inner tube facing the reflector. The heat flux density on the sun-facing side can reach over 100 kW / m², with extremely high temperatures; while the shaded side receives almost no concentrated radiation, resulting in significantly lower temperatures. Engineering operation data shows that the circumferential temperature difference of the metal inner tube in traditional collector tubes can reach 80-120℃, generating thermal stress. Under long-term operation, this leads to fatigue deformation, bending cracks, and air leakage at the glass-metal seal, ultimately causing vacuum failure and collector tube scrapping. This type of failure accounts for more than 60% of the operational failures of parabolic trough collector tubes.

[0005] 2) Poor flow conditions of the heat transfer medium inside the tube result in low heat exchange efficiency, further exacerbating local overheating problems. The flow of the heat transfer medium inside the trough-type heat collector tube is mostly laminar or weakly turbulent. The flow boundary layer and thermal boundary layer inside the tube are relatively thick, and the radial thermal conductivity and mixing capacity of the fluid are extremely weak. The heat from the hot spot on the sun-facing side cannot be quickly transferred to the fluid interior and the shaded side, further aggravating local overheating and circumferential temperature difference, while also leading to a low overall photothermal conversion efficiency.

[0006] 3) Currently used improvement methods such as baffles, internal inserts, and enhanced fluid have problems such as high resistance, uneven mixing, easy clogging, and poor reliability. At the same time, internal inserts have problems such as easy clogging, easy coking, difficult installation and maintenance, and poor long-term operational reliability. Moreover, they can only enhance axial mixing and cannot fundamentally solve the core problem of uneven circumferential temperature, resulting in very limited heat equalization effect.

[0007] Taylor-Couette-Poiseuille flow occurs when concentric cylinders rotate relative to each other while axial flow occurs. Under shearing action, the fluid forms Taylor vortices. Theoretical and experimental studies show that this flow pattern enhances radial mixing, effectively reduces circumferential temperature non-uniformity, and improves convective heat transfer efficiency. Currently, this technology has not been implemented in commercially available trough-type vacuum solar collector tubes. The core bottlenecks lie in the lack of a suitable flow path design adapted to the axial flow conditions of the collector tube, a reliable operating structure for the rotating inner core tube, and a rotation speed control method that matches the varying illumination conditions of the collector tube.

[0008] Existing rotary heat transfer enhancement technologies mostly employ structures such as built-in rotating blades, turbulent rotors, or helical inserts, primarily enhancing axial mixing heat transfer through random fluid disturbance. These technologies typically suffer from uncontrollable rotational speed, high local resistance, susceptibility to coking and blockage, and insufficient long-term operational reliability. Furthermore, the resulting flow structures are often unstable turbulent eddies, making it difficult to achieve regular radial periodic mixing within annular channels. This hinders the effective homogenization of the circumferential temperature distribution in trough-type solar collectors under non-uniform solar heat flow, thus failing to fundamentally address the thermal stress failure problem of the metal heat-absorbing inner tubes. Summary of the Invention

[0009] To address the aforementioned technical problems, this invention provides a trough-type solar vacuum collector tube with a rotating inner core structure. This is a vacuum collector tube with adaptive operating conditions for use in trough solar collector systems. It utilizes Taylor-Couette-Poiseuille flow to enhance heat transfer, homogenize wall temperature, and adapt to different solar radiation conditions. This invention introduces Taylor-Couette-Poiseuille flow into the annular flow channel of the trough-type solar vacuum collector tube, inducing a radially periodic vortex structure using the rotating inner core tube. This achieves active heat homogenization and wall temperature homogenization under circumferential heat flow unevenness, while adapting to operating conditions with different solar radiation intensities.

[0010] This invention achieves dynamic and precise adjustment of the inner core tube's rotational speed through a variable frequency geared motor and a closed-loop speed control module, ensuring that an appropriate speed is maintained under varying lighting conditions. The combination of a uniform annular inlet structure at the drive end and an end sealing assembly provides a stable axial flow channel for the heat transfer medium. The segmented metal heat-absorbing inner tube, coupled with radial support bearings, ensures uniform annular flow channel clearance, providing stable geometric boundary conditions for the regular generation of Taylor vortices. Furthermore, it compensates for axial thermal expansion deformation under high-temperature conditions, preventing tube bending deformation and improving long-term operational reliability.

[0011] The hollow rotating inner core tube adopts an integrated, seamless, closed hollow structure with sealed welds at both ends. It does not serve as a flow channel for the heat transfer medium, significantly reducing rotational inertia while ensuring structural rigidity. This adapts to wide-range, stable speed regulation requirements and avoids the risk of corrosion and coking caused by the medium entering the inner cavity. The bent-tube inlet assembly includes a fixed bent tube and a coaxial dynamic seal structure. The heat transfer medium enters the annular flow channel through the fixed bent tube, and the hollow rotating inner core tube extends through the coaxial dynamic seal structure to the outside of the tube and connects to the drive system.

[0012] Based on this, the coaxial rotating inner core tube is coupled with the annular flow channel to form a Taylor-Couette-Poiseuille flow structure. Under appropriate rotation speed and axial flow conditions, regular Taylor vortices are induced to form. Through stable radial mixing, circumferential heat transfer is enhanced, and the synergistic control of circumferential temperature uniformity and enhanced heat transfer of the heat collection tube is achieved.

[0013] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0014] A trough-type solar vacuum collector tube with a rotating inner core structure includes a glass outer tube, a metal heat-absorbing inner tube, a hollow rotating inner core tube, an end sealing assembly, a bent tube inlet assembly, and an active drive and speed control system;

[0015] The inner metal heat-absorbing tube is disposed inside the outer glass tube, and a closed high-vacuum heat insulation layer is formed between the inner metal heat-absorbing tube and the outer glass tube; the outer wall of the inner metal heat-absorbing tube is provided with a solar selective absorption coating.

[0016] The hollow rotating inner core tube is disposed inside the metal heat-absorbing inner tube and is arranged coaxially with the metal heat-absorbing inner tube, and an annular flow channel for the flow of heat transfer medium is formed between the hollow rotating inner core tube and the metal heat-absorbing inner tube.

[0017] The end sealing components are respectively disposed at the driving end and the non-driving end of the metal heat-absorbing inner tube;

[0018] The bend inlet assembly is connected to the end sealing assembly located at the drive end, and the end sealing assembly at the non-drive end is provided with a heat transfer medium outlet.

[0019] The active drive and speed control system is used to drive the hollow rotating inner core tube to rotate.

[0020] The heat transfer medium enters the annular flow channel through the bent inlet assembly, flows axially along the annular flow channel, and flows out through the heat transfer medium outlet. When the hollow rotating inner core tube rotates, it drives the heat transfer medium in the annular flow channel to form a rotating flow.

[0021] In the above scheme, the hollow rotating inner core tube has a closed cavity structure inside.

[0022] In the above scheme, the metal heat-absorbing inner tube adopts a segmented structure including multiple tube segments, and adjacent tube segments are sealed together; the inner wall of the metal heat-absorbing inner tube is provided with radial support bearings at the joints of each segment to support the hollow rotating inner core tube and maintain the coaxiality between the hollow rotating inner core tube and the metal heat-absorbing inner tube.

[0023] In the above scheme, the end sealing assembly of the drive end is provided with an annular medium inlet, and the heat transfer medium enters the annular flow channel uniformly along the circumference of the annular medium inlet.

[0024] Furthermore, the bend inlet assembly includes a fixed bend and a coaxial mechanical seal;

[0025] One end of the fixed bend is connected to the end sealing assembly on the drive side, and the other end is provided with a heat transfer medium inlet.

[0026] The coaxial mechanical seal is located at the central through hole of the fixed bend; the drive end of the hollow rotating inner core tube passes through the coaxial mechanical seal and is connected to the active drive and speed control system via the coupling.

[0027] In the above scheme, the active drive and speed control system includes a variable frequency geared motor, a temperature sensor, a direct radiation meter, a controller, and a frequency converter;

[0028] The variable frequency geared motor is connected to the drive end of the hollow rotating inner core tube via the coupling, and is used to drive the hollow rotating inner core tube to rotate; the temperature sensor is evenly arranged along the outer wall of the metal heat-absorbing inner tube to detect the circumferential temperature difference of the metal heat-absorbing inner tube; the direct radiation meter is used to detect the solar radiation intensity.

[0029] The controller is connected to the temperature sensor, the direct radiation meter and the frequency converter respectively. The frequency converter is electrically connected to the variable frequency geared motor. The controller adjusts the speed of the variable frequency geared motor through the frequency converter according to the solar radiation intensity and the circumferential temperature difference to drive the hollow rotating inner core tube to rotate.

[0030] Furthermore, the temperature sensors are Pt100 temperature sensors, and there are four of them;

[0031] Four Pt100 temperature sensors are evenly arranged circumferentially along the outer wall of the metal heat-absorbing inner tube, with an included angle of 90° between adjacent sensors. They are used to detect the circumferential temperature difference of the metal heat-absorbing inner tube and transmit the data to the controller.

[0032] Furthermore, the controller has a built-in speed closed-loop control module;

[0033] The speed closed-loop control module uses the speed determined based on solar radiation intensity as the reference speed and performs proportional-integral regulation based on the circumferential temperature difference to correct the speed of the hollow rotating inner core tube. When the circumferential temperature difference exceeds the preset temperature difference dead zone, the controller increases the speed of the variable frequency reduction motor according to the proportional-integral law. When the circumferential temperature difference falls back to within the preset temperature difference dead zone, the controller controls the speed of the variable frequency reduction motor to maintain or restore the reference speed, so as to drive the hollow rotating inner core tube to rotate at the target speed.

[0034] In the above scheme, the outer radius of the hollow rotating inner core tube is 1 / 2 of the inner radius of the metal heat-absorbing inner tube.

[0035] In the above scheme, when the hollow rotating inner core tube rotates, a Taylor-Couette-Poiseuille flow is formed in the annular flow channel. Through radial mixing of the fluid and circumferential heat transport, the circumferential temperature difference of the metal heat-absorbing inner tube is reduced and the thermal stress is decreased.

[0036] Compared with the prior art, the beneficial effects of the present invention are:

[0037] This invention enables the heat transfer medium to enter the annular flow channel uniformly along the circumference through the annular medium inlet of the end sealing assembly of the drive end, achieving undisturbed entry of the medium into the annular flow channel. Combined with a segmented metal inner tube, this ensures uniform gaps in the annular flow channel, allowing the Taylor-Couette-Poiseuille flow structure to form within the annular flow channel. Through the strong radial mixing effect of regular Taylor vortices, the circumferential temperature distribution of the metal heat-absorbing inner tube can be effectively homogenized. Under the typical operating conditions applicable to this invention (such as the heat transfer oil at 300°C or the molten salt at 550°C in the embodiment), the circumferential temperature difference can be reduced by more than 30%, thereby significantly reducing cyclic thermal stress and extending the service life of the heat collector tube. Simultaneously, it continuously smooths out radial temperature stratification of the fluid (due to the Taylor vortices in the Taylor-Couette-Poiseuille flow continuously carrying the high-temperature fluid from the outer wall into the interior and the low-temperature fluid from the interior to the outer wall through radial-axial cyclic movement, thus continuously exchanging the fluid in the radial position and making the radial temperature distribution tend to be uniform), achieving uniform outlet medium temperature and effectively improving the operational stability of the downstream heat system.

[0038] This invention continuously disrupts the flow and thermal boundary layers through the formed rotating vortex structure, resulting in an improved convective heat transfer coefficient inside the tube compared to traditional collector tubes. Unlike the random turbulent flow formed by traditional rotating turbulence inserts, the Taylor vortex formed in this invention exhibits periodic radial mixing characteristics, simultaneously enhancing circumferential heat transport and radial fluid mixing. Combined with adaptive rotation speed control based on the intensity of direct solar radiation and the circumferential temperature difference of the inner metal tube, the overall system energy efficiency can be improved under all operating conditions, enhancing the system's circulation efficiency. The hollow rotating inner core tube structure used in this invention ensures that only the outer wall of the inner core tube contacts the heat transfer medium, effectively avoiding the risks of corrosion, coking, and high-temperature vaporization caused by the medium entering the inner cavity. The dynamic seal at the drive end only contacts the low-temperature inlet medium, significantly improving the working environment and further enhancing the long-term reliability of the device. The segmented metal heat-absorbing inner tube structure used in this invention effectively solves the problems of coaxiality control during long tube processing and high-temperature axial thermal expansion deformation, making it suitable for various application scenarios such as medium- and low-temperature industrial heating and high-temperature solar thermal power generation, possessing good engineering adaptability and promotional application value. This invention achieves dynamic matching between the Taylor-Couette-Poiseuille flow and solar radiation conditions through light-adaptive rotation speed control. It enhances heat exchange and heat homogenization under strong light and reduces drive energy consumption under weak light, thereby improving the overall energy efficiency of the system. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the overall axial full section structure of a trough-type solar vacuum collector tube according to an embodiment of the present invention.

[0040] Explanation of reference numerals in the attached drawings: 1—outer glass tube; 2—high vacuum insulation layer; 3—segmented metal heat-absorbing inner tube; 4—solar selective absorption coating; 5—annular flow channel; 6—hollow rotating inner core tube; 7—end sealing assembly; 8—radial support bearing; 9—heat transfer medium inlet; 10—heat transfer medium outlet; 11—fixed bend; 12—coaxial mechanical seal; 13—annular medium inlet. Detailed Implementation

[0041] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0042] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "front," "rear," "left," "right," "upper," "lower," "axial," "radial," "vertical," "horizontal," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0043] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0044] Figure 1 The diagram shows a preferred embodiment of the trough solar vacuum collector tube with a rotating inner core structure. The trough solar vacuum collector tube with a rotating inner core structure includes a glass outer tube 1, a metal heat-absorbing inner tube 3, a hollow rotating inner core tube 6, an end sealing assembly 7, a bent tube inlet assembly, and an active drive and speed control system.

[0045] The inner metal heat-absorbing tube 3 is disposed inside the outer glass tube 1, and the outer wall of the inner metal heat-absorbing tube 3 is provided with a solar selective absorption coating 4; the hollow rotating inner core tube 6 is disposed inside the inner metal heat-absorbing tube 3 and is coaxially arranged with the inner metal heat-absorbing tube 3, and an annular flow channel 5 for unidirectional axial flow of the heat transfer medium is formed between the hollow rotating inner core tube 6 and the inner metal heat-absorbing tube 3; the end sealing components 7 are respectively disposed at the driving end and the non-driving end of the inner metal heat-absorbing tube 3; the bent tube inlet component is connected to the end sealing component 7 located at the driving end, and the bent tube inlet component is used to uniformly input the heat transfer medium into the annular flow channel, and the end... The sealing assembly 7 is used to achieve end sealing between the sealed glass outer tube (1) and the metal heat-absorbing inner tube (3) to maintain the vacuum sealing of the high vacuum insulation layer (2); the end sealing assembly 7 at the non-driving end is provided with a heat transfer medium outlet 10; the active drive and speed control system is used to drive the hollow rotating inner core tube 6 to rotate; the heat transfer medium enters the annular flow channel 5 through the bent pipe inlet assembly, flows along the axial direction of the annular flow channel 5, and flows out through the heat transfer medium outlet 10. When the hollow rotating inner core tube 6 rotates, it drives the heat transfer medium in the annular flow channel 5 to form a rotating flow, so as to enhance the radial mixing of the fluid and the circumferential heat transport.

[0046] The hollow rotating inner core tube 6 is a one-piece seamless hollow structure; the interior of the hollow rotating inner core tube 6 is a closed cavity structure and does not serve as a channel for the flow of heat transfer medium. The entire hollow rotating inner core tube 6 is uniformly seamless and hollow, with both ends of the tube being sealed and welded, and the inner cavity is completely closed and has no medium flow function;

[0047] The metal heat-absorbing inner tube 3 adopts a segmented structure comprising multiple tube segments, with adjacent tube segments sealed together. The inner wall of the metal heat-absorbing inner tube 3 is provided with radial support bearings 8 at the joints of each segment to support the hollow rotating inner core tube 6 and maintain the coaxiality between the hollow rotating inner core tube 6 and the metal heat-absorbing inner tube 3.

[0048] In one specific embodiment of the present invention, the metal heat-absorbing inner tube 3 is divided into 2-3 segments, with adjacent segments connected by a sealed connection to ensure the coaxiality and sealing performance of the entire inner wall of the tube. Radial support bearings 8 are installed on the inner wall of the tube at the joints of each segment, providing radial support to the hollow rotating inner core tube 6 and maintaining uniform gaps in the annular flow channel 5, which is beneficial for the formation of the Taylor-Couette-Poiseuille flow structure. The segmented structure can effectively compensate for the axial thermal expansion difference under high-temperature conditions, avoid tube bending deformation, and improve long-term operational reliability.

[0049] The geometry of the annular flow channel 5 matches the rotational and axial flow conditions of the inner core tube, facilitating the formation of a Taylor-Couette-Poiseuille flow structure. The total axial length of the hollow rotating inner core tube 6 is basically the same as that of the metal heat-absorbing inner tube 3. The end face of the non-driving end is flush with the inner wall of the non-driving end of the metal heat-absorbing inner tube 3. The driving end is an extended hollow shaft extension section. The outer wall of this shaft extension section is precision machined and extends to the outside of the tube through the end sealing assembly 7 and the bent inlet assembly for transmission connection with the rotating drive device. While ensuring structural rigidity and torsional strength, the hollow rotating inner core tube 6 significantly reduces the self-weight and rotational inertia of the inner core tube. The variable frequency motor can achieve smooth speed regulation over a wide range. At the same time, only the outer wall of the inner core tube is in contact with the heat transfer medium, effectively reducing the risk of corrosion, coking, and high-temperature vaporization caused by the medium entering the inner cavity, and improving long-term operational reliability.

[0050] The end sealing assembly 7 is located at both axial ends of the metal heat-absorbing inner tube 3, and is divided into a driving-side end sealing assembly 7 and a non-driving-side end sealing assembly 7. The non-driving-side end sealing assembly 7 has a coaxial medium outlet 10, which is sealed to the non-driving end of the metal heat-absorbing inner tube 3 through an inner tube positioning flange, fasteners, and static seals. The heat-exchanged medium flows out through this outlet. The driving-side end sealing assembly 7 has an annular medium inlet 13, which is sealed to the bend inlet assembly, providing a 360° uniform flow path for the heat transfer medium to enter the annular flow channel 5. The heat transfer medium enters the annular flow channel 5 uniformly along the circumference of the annular medium inlet 13 to reduce local flow deviation at the inlet.

[0051] The bend-inlet assembly includes a fixed bend 11 and a coaxial mechanical seal 12. One end of the fixed bend 11 is connected to the end sealing assembly 7 on the drive side, and the other end is provided with a heat transfer medium inlet 9 to achieve uniform entry of the low-temperature medium into the annular flow channel 5. The coaxial mechanical seal 12 is located at the central through hole of the fixed bend 11. The drive end of the hollow rotating inner core tube 6 passes through the coaxial mechanical seal 12 and is connected to the active drive and speed control system via the coupling. Specifically, the hollow shaft extension of the drive end of the hollow rotating inner core tube 6 extends through the coaxial mechanical seal 12 to the outside of the fixed bend 11. The coaxial mechanical seal 12 is located at the central through hole of the fixed bend 11 to achieve dynamic sealing between the hollow rotating inner core tube 6 and the fixed bend 11, ensuring smooth rotation of the inner core tube and good sealing of the medium cavity.

[0052] This invention optimizes the processing and installation performance of the tube body through a segmented metal inner tube 3, ensures the rotation drive stiffness and reduces the moment of inertia through an integrated hollow rotating inner core tube 6, enables the medium to directly enter the annular flow channel 5 for stable rotation through the drive end bend inlet assembly, and achieves wide-range stable and precise speed regulation of the hollow rotating inner core tube 6 through coaxial direct transmission of the coupling, ultimately realizing enhanced heat transfer inside the tube, homogenization of circumferential wall temperature and uniformity of outlet medium temperature.

[0053] The active drive and speed control system includes a variable frequency geared motor, a temperature sensor, a direct radiation meter, a controller, and a frequency converter. The variable frequency geared motor is connected to the drive end of the hollow rotating inner tube 6 via the coupling, and is used to drive the hollow rotating inner tube 6 to rotate. The temperature sensor is evenly arranged circumferentially along the outer wall of the metal heat-absorbing inner tube 3, and is used to detect the circumferential temperature difference of the metal heat-absorbing inner tube 3. The direct radiation meter is used to detect the solar radiation intensity. The controller is connected to the temperature sensor, the direct radiation meter, and the frequency converter respectively, and the frequency converter is electrically connected to the variable frequency geared motor. The controller adjusts the speed of the variable frequency geared motor through the frequency converter according to the solar radiation intensity and the circumferential temperature difference, so as to drive the hollow rotating inner tube 6 to rotate.

[0054] The hollow shaft extension of the drive end of the hollow rotating inner core tube 6 is directly connected to the output shaft of the variable frequency geared motor through a coupling. The motor shaft and the inner core tube axis are arranged coaxially, which effectively reduces the risk of spatial interference between the motor and the heat collection tube body and the inlet and outlet liquid pipelines. The transmission efficiency is higher and the structure is more compact. At the same time, it achieves stable speed reduction and torque increase, which is suitable for the low-speed and high-torque operation requirements of the inner core tube.

[0055] The temperature sensors are Pt100 temperature sensors, and there are four of them. The four Pt100 temperature sensors are evenly arranged around the outer wall of the metal heat-absorbing inner tube 3, with an included angle of 90° between adjacent sensors. They are used to detect the circumferential temperature difference of the metal heat-absorbing inner tube 3 and transmit it to the controller.

[0056] The controller has a built-in speed closed-loop control module. The speed closed-loop control module uses the speed determined based on the solar radiation intensity as the reference speed and performs proportional-integral regulation based on the circumferential temperature difference to correct the speed of the hollow rotating inner core tube 6. When the circumferential temperature difference exceeds the preset temperature difference dead zone, the controller increases the speed of the variable frequency reduction motor according to the proportional-integral law. When the circumferential temperature difference falls back to within the preset temperature difference dead zone, the controller controls the speed of the variable frequency reduction motor to maintain or restore the reference speed, so as to drive the hollow rotating inner core tube 6 to rotate at the target speed.

[0057] The outer radius of the hollow rotating inner core tube 6 is half the inner radius of the metal heat-absorbing inner tube 3. Setting the outer radius of the inner core tube to half the inner radius of the heat-absorbing inner tube has two advantages: firstly, it forms an annular gap that matches the Taylor-Couette-Poiseuille flow, stably generating regular Taylor vortices and achieving efficient radial mixing of the fluid and uniform transport of circumferential heat from the tube wall; secondly, it reserves sufficient cross-sectional area for medium flow, avoiding excessively narrow flow channels that would restrict medium flow and significantly increase flow resistance.

[0058] When the hollow rotating inner tube 6 rotates, a rotating shear flow structure is formed in the annular flow channel 5. When the rotational speed of the hollow rotating inner tube is higher than the critical speed for the formation of Taylor vortex, Taylor-Couette-Poiseuille flow is formed. Through radial mixing of fluid and circumferential heat transport, the circumferential temperature difference of the metal heat-absorbing inner tube 3 is reduced and the thermal stress is decreased.

[0059] Example 1

[0060] This embodiment is suitable for medium and low temperature industrial heating scenarios. The heat transfer medium is hydrogenated terphenyl heat transfer oil, with a maximum operating temperature of 300℃. The core structure includes a glass outer tube 1, a metal heat-absorbing inner tube 3, a hollow rotating inner core tube 6, an end sealing assembly 7, a bent inlet assembly, and an active drive and speed control system.

[0061] The supporting basic heat collection unit adopts a domestically commercially available 70mm diameter trough-type vacuum heat collection tube structure. The transparent glass outer tube 1 is made of high borosilicate tempered glass. The segmented metal heat-absorbing inner tube 3 is divided into two sections, each 2000mm long, 70mm in inner diameter, and 2mm thick. Matching flanges are welded between the two sections, and a sealed connection is achieved using bolts and metal-coated fluororubber sealing rings, ensuring the overall pressure resistance and media sealing performance of the tube. Radial support bearings 8 are installed at the segment joints to provide radial support for the hollow rotating inner core tube 6, ensuring a coaxiality error ≤0.02mm throughout the entire process. The outer wall of the metal heat-absorbing inner tube 3 is coated with a high-temperature solar selective absorption coating 4, with a solar absorptivity of 0.96 and an infrared emissivity of 0.07. A high-vacuum insulation layer 2 is formed between the metal heat-absorbing inner tube 3 and the glass outer tube 1, with a vacuum degree better than 5×10⁻⁶. -4 Pa.

[0062] The hollow rotating inner core tube 6 is a one-piece hollow structure made of 316L stainless steel. Its outer diameter matches the inner diameter of the metal heat-absorbing inner tube 3 to form an annular flow channel 5 for enhancing radial mixing and circumferential heat exchange of the fluid. The entire tube is formed from the same seamless tubing, and both ends are fully sealed by argon arc welding. After welding, it passes the airtightness test. The inner cavity is closed and there are no medium flow channels. The total axial length of the hollow rotating inner core tube 6 is basically the same as the total axial length of the metal heat-absorbing inner tube 3. The end face of the non-driving end is flush with the inner wall of the non-driving end of the metal heat-absorbing inner tube 3. The driving end is an extended hollow shaft extension. The outer wall of the shaft extension is precision machined, and the surface finish meets the requirements of dynamic sealing and coupling installation. This shaft extension extends to the outside of the tube through the coaxial mechanical seal of the bent tube inlet assembly. An annular flow channel 5 is formed between the outer wall of the hollow rotating inner core tube 6 and the inner wall of the metal heat-absorbing inner tube 3.

[0063] End sealing components 7 are located at both ends of the metal heat-absorbing inner tube 3. The non-drive side end sealing component 7 has a coaxial medium outlet 10, which is sealed to the non-drive end of the metal heat-absorbing inner tube 3. The drive side end sealing component 7 has an annular medium inlet 13, which is sealed to the bend inlet component. The end sealing component 7 includes an inner tube positioning flange, a sealing end cover body, fasteners, and static sealing components. The inner tube positioning flange is made of 316L stainless steel, the same material as the metal heat-absorbing inner tube 3. It is fitted onto the outer wall of the end of the metal heat-absorbing inner tube 3 with a precision transition fit of H7 / k6, and is sealed and fixed by circumferential welding. The sealing end cover body and the inner tube positioning flange are fastened diagonally by 12 M8 double-ended bolts. A metal-coated fluororubber sealing ring is set between them to achieve static sealing of the heat transfer medium cavity inside the metal heat-absorbing inner tube. The outer side of the sealing end cover body is provided with There is a coaxial limiting stop that matches the outer diameter of the glass outer tube 1. The end of the glass outer tube 1 is inserted into the limiting stop to achieve automatic centering. A vacuum-specific fluororubber sealing ring is set between the end face of the glass outer tube 1 and the sealing end cap body to seal the high vacuum insulation layer 2 and maintain the vacuum level. The sealing end cap bodies at both ends are pre-tightened by circumferentially evenly arranged long tie rod bolts. A high-temperature wave spring washer is installed between the long tie rod bolts and the mounting end face of the sealing end cap body to automatically compensate for the axial thermal expansion difference between the metal heat-absorbing inner tube and the glass outer tube and maintain a stable pre-tightening force on the sealing surface.

[0064] The bend inlet assembly includes a 90° fixed bend 11 and a universal welded metal bellows mechanical seal 12. The fixed bend 11 is made of 316L stainless steel. One end is welded to the annular medium inlet 13 of the drive-side end sealing assembly 7, and the other end serves as the heat transfer medium inlet 9. A coaxial through hole is opened at the center of the outer end face of the fixed bend 11. The mechanical seal 12 is press-fitted into the through hole. The hollow shaft extension of the drive end of the hollow rotating inner core tube 6 extends through the mechanical seal 12 to the outside of the fixed bend 11. The mechanical seal 12 only contacts the outer wall of the precision-machined shaft extension of the drive end of the hollow rotating inner core tube 6 to achieve a stable dynamic seal.

[0065] The rotary drive unit is a 0.75kW variable frequency geared motor with a rated speed range of 0-100rpm, compatible with 380V industrial power supply. The hollow shaft extension at the drive end of the hollow rotating inner tube 6 is coaxially connected to the motor output shaft via a coupling. The motor is fixed to the end truss of the heat collector tube via an independent mounting bracket, sharing the same mounting foundation with the heat collector tube. The controller is a PLC controller. Four Pt100 temperature sensors are evenly arranged circumferentially along the outer wall of the metal heat-absorbing inner tube 3, with an included angle of 90° between adjacent sensors, located at 0° (center of the light-facing side), 90°, 180° (center of the shadow-facing side), and 270° respectively. The sensors are installed in the middle region of the outer wall of the metal heat-absorbing inner tube 3, specifically at 1 / 3 of the total length from the drive end of the heat collector tube. This position is located in the fully developed section of the annular flow channel 5, avoiding the influence of end effects, and can accurately reflect the circumferential temperature distribution characteristics, possessing good response sensitivity and representativeness. The rotation speed can be adjusted in real time based on the direct solar radiation intensity and the circumferential temperature difference of the metal heat-absorbing inner tube 3. The following empirical function relationship is established between the direct solar radiation intensity (DNI) and the target rotation speed of the hollow rotating inner tube 6, which serves as the basic setting for the rotation speed closed-loop control module:

[0066]

[0067] Where: n target n is the target rotational speed (rpm); min = 2rpm, n max = 100 rpm; DNI min =200W / m 2 , DNI max = 1000 W / m 2 ;Δn(T circ The value is a rotational speed correction term based on the circumferential temperature difference of the metal heat-absorbing inner tube. This functional relationship was established through a combination of theoretical analysis, numerical simulation, and experimental verification. After cross-validation with multiple sets of experimental data, the relative error between the predicted and measured values ​​is within ±8%, which meets the engineering control accuracy requirements.

[0068] The speed closed-loop control module employs a proportional-integral (PI) regulation strategy, using the circumferential temperature difference ΔT within the metal heat-absorbing inner tube to correct the target speed in real time. The circumferential temperature difference ΔT is defined as the difference between the maximum and minimum temperatures measured by the four Pt100 sensors. The correction term Δn(T) circ The expression for ) is:

[0069] When ΔT ≤ ΔT dead When Δn = 0; when ΔT > ΔT dead hour

[0070]

[0071] Where: ΔT dead = 5℃ is the adjustment dead zone; speed adjustment is not performed when the temperature difference is less than or equal to 5℃ to avoid control oscillation; K p = 2 rpm / ℃ is the proportional gain; for every 1℃ increase in temperature beyond the dead zone, the engine speed increases by 2 rpm; K i = 0.1 rpm / (℃·s) is the integral gain, used to eliminate steady-state temperature difference accumulation, and t is the system running time. The control system's adjustment response time is 10 seconds, meaning the delay from when the sensor detects a temperature difference change to when the speed adjustment begins does not exceed 10 seconds. When the calculated target speed exceeds 100 rpm, the controller automatically limits it to 100 rpm; when it is below 2 rpm, it operates at 2 rpm.

[0072] In a specific embodiment of the present invention, when DNI is 800 W / m 2 At this point, the baseline target speed is approximately 65 rpm. If the measured circumferential temperature difference is 30°C, exceeding the dead zone of 25°C, the speed correction is 2 × 25 = 50 rpm, resulting in a final target speed of 115 rpm. After limiting, it operates at 100 rpm. When the temperature difference drops below 10°C, the speed gradually recovers to the baseline target value. In this embodiment, the speed closed-loop control module adjusts the speed of the inner core tube 6.

[0073] The working flow path of this embodiment is as follows: Low-temperature heat transfer oil flows in from the heat transfer medium inlet 9 of the fixed bend tube 11 on the drive side, and enters the annular flow channel 5 uniformly at 360° through the annular medium inlet 13 of the end sealing assembly 7 on the drive side. It flows unidirectionally along the axis of the annular flow channel 5 to the non-drive end. Under the shearing action of the hollow rotating inner core tube 6, it forms a rotating shear flow state, which enhances the radial mixing of the fluid and the circumferential heat transport. Finally, it flows out through the medium outlet 10 of the end sealing assembly 7 on the non-drive side and enters the next section of the heat collection tube.

[0074] Example 2

[0075] This embodiment is adapted to high-temperature solar thermal power generation scenarios. The heat transfer medium is binary nitrate molten salt, with a maximum operating temperature of 550°C. The core structure is the same as that of Embodiment 1 (including glass outer tube 1, metal heat-absorbing inner tube 3, hollow rotating inner core tube 6, end sealing assembly 7, bent tube inlet assembly, and active drive and speed control system), with only adaptation adjustments made for high-temperature operating conditions.

[0076] In this embodiment, both the metal heat-absorbing inner tube 3 and the hollow rotating inner core tube 6 are made of Hastelloy C276. The metal heat-absorbing inner tube 3 is divided into 3 sections, each with a length of 2000mm, an inner diameter of 70mm, and a wall thickness of 3mm. Preferably, the outer radius of the hollow rotating inner core tube 6 is half the inner radius of the metal heat-absorbing inner tube 3, and both ends of the tube are fully sealed by argon arc welding, making the inner cavity completely closed. The radial support bearing 8 is made of high-temperature alloy. The dynamic sealing structure uses a combination of 4 layers of high-temperature resistant flexible graphite packing rings for sealing, with a temperature resistance of ≥650℃. The static sealing element uses an Inconel alloy C-type metal sealing ring. The variable frequency geared motor has a rated power of 1.5kW and a rated speed range of 0-100rpm.

[0077] The critical rotational speed for Taylor vortex formation is estimated as follows:

[0078] Based on the critical Reynolds number Re for the inner cylinder where Taylor vortices appear. c Re c ≈41.3 (R) i / d) -0.5；

[0079] Where: R i : Inner cylinder radius; Annular gap width d=R o -R i ;R o Outer cylinder radius;

[0080] Critical Reynolds number for inner cylinder: Re i =ωR i d / ν;

[0081] Where: ω: angular velocity (rad / s); ν: kinematic viscosity;

[0082] Critical angular velocity: ω c =Re c ν / (R i d);

[0083] Critical speed (rpm): n c =30Re c ν / (3.14R i d);

[0084] Based on implementation cases: R i =17.5mm, R o=35mm, d=17.5mm;

[0085] After substituting the values, Re is calculated. c ≈41.3;

[0086] At 550°C, the kinematic viscosity of the molten salt is: ν = 1.11 × 10⁻⁶ -6 m 2 / s;

[0087] After substituting: ω c ≈0.15rad / s, n c ≈1.43 rpm;

[0088] When the rotational speed of the hollow rotating inner tube 6 is higher than the critical speed for the formation of the Taylor vortex, a Taylor-Couette-Poiseuille flow structure can be formed in the annular flow channel 5, thereby enhancing the radial mixing and circumferential heat transport of the fluid.

[0089] Based on the above calculations, in this embodiment, the speed closed-loop control module adjusts the speed of the hollow rotating inner tube 6 within the range of 2 rpm to 100 rpm. Its control strategy is the same as in Embodiment 1, that is, it adopts the same DNI-speed function relationship and PI adjustment rule. Specifically, the proportional gain K... p = 2 rpm / ℃, integral gain K i = 0.1 rpm / (℃·s), adjust dead zone ΔT dead = 5℃, response time 10 seconds. When the circumferential temperature difference ΔT of the inner metal heat-absorbing tube 3 exceeds the dead zone, the controller automatically increases the rotation speed according to the above rules; when the temperature difference drops, the rotation speed gradually decreases. In this embodiment, under high-temperature conditions of 550℃, a rotating shear flow structure can be formed in the annular flow channel 5, enhancing the radial mixing of the fluid and the circumferential heat transport, effectively avoiding local overheating and coking of the molten salt, ensuring stable and reliable operation, and suitable for the operating conditions of large-scale parabolic trough solar thermal power plants.

[0090] In this invention, a hollow rotating inner core tube 6 and a metal heat-absorbing inner tube 3 are arranged coaxially to form an annular flow channel 5. The outer radius of the hollow rotating inner core tube 6 is half the inner radius of the metal heat-absorbing inner tube 3. The heat transfer medium enters the annular flow channel 5 through the bent tube inlet assembly and flows axially. The rotating inner core tube 6 rotates under the drive of an active drive and speed control system, causing the heat transfer medium to form a rotating shear flow. The end sealing assembly 7 of the drive end is provided with an annular medium inlet 13, and the heat transfer medium enters the annular flow channel 5 uniformly along the circumference. The active drive and speed control system adjusts the speed in real time according to the solar radiation intensity and the circumferential temperature difference. This invention can effectively homogenize the circumferential temperature distribution of the metal heat-absorbing inner tube 3, reduce the circumferential temperature difference, and reduce thermal stress, making it suitable for medium and low temperature industrial heating and high temperature solar thermal power generation scenarios.

[0091] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0092] The detailed descriptions listed above are merely specific illustrations of feasible embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A slot-type solar vacuum heat collecting tube having a rotating inner core structure, characterized in that, It includes a glass outer tube (1), a metal heat-absorbing inner tube (3), a hollow rotating inner core tube (6), an end sealing assembly (7), a bent tube inlet assembly, and an active drive and speed control system; The metal heat-absorbing inner tube (3) is disposed inside the glass outer tube (1), and a closed high vacuum heat insulation layer (2) is formed between the metal heat-absorbing inner tube (3) and the glass outer tube (1); the outer wall of the metal heat-absorbing inner tube (3) is provided with a solar selective absorption coating (4). The hollow rotating inner core tube (6) is disposed inside the metal heat-absorbing inner tube (3) and is arranged coaxially with the metal heat-absorbing inner tube (3), and an annular flow channel (5) for the flow of heat transfer medium is formed between the hollow rotating inner core tube (6) and the metal heat-absorbing inner tube (3). The end sealing components (7) are respectively disposed at the driving end and the non-driving end of the metal heat-absorbing inner tube (3); The bend inlet assembly is connected to the end sealing assembly (7) located at the drive end, and the end sealing assembly (7) at the non-drive end is provided with a heat transfer medium outlet (10). The active drive and speed control system is used to drive the hollow rotating inner core tube (6) to rotate; The heat transfer medium enters the annular flow channel (5) through the bent inlet assembly and flows axially along the annular flow channel (5), and flows out through the heat transfer medium outlet (10). When the hollow rotating inner core tube (6) rotates, it drives the heat transfer medium in the annular flow channel (5) to form a rotating flow.

2. The evacuated tube solar collector according to claim 1, wherein, The hollow rotating inner core tube (6) has a closed cavity structure inside.

3. The evacuated tube solar collector according to claim 1, wherein, The metal heat-absorbing inner tube (3) adopts a segmented structure, including multiple tube segments, with adjacent tube segments sealed together; the inner wall of the metal heat-absorbing inner tube (3) is provided with radial support bearings (8) at the joints of each segment, which are used to support the hollow rotating inner core tube (6) and maintain the coaxiality between the hollow rotating inner core tube (6) and the metal heat-absorbing inner tube (3).

4. The evacuated tube solar collector according to claim 1, wherein, The end sealing assembly (7) of the drive end is provided with an annular medium inlet (13), and the heat transfer medium enters the annular flow channel (5) uniformly along the circumference of the annular medium inlet (13).

5. The trough-type solar vacuum collector tube with a rotating inner core structure according to claim 4, characterized in that, The bend inlet assembly includes a fixed bend (11) and a coaxial mechanical seal (12). One end of the fixed bend (11) is connected to the end sealing assembly (7) on the drive side, and the other end is provided with a heat transfer medium inlet (9). The coaxial mechanical seal (12) is located at the central through hole of the fixed bend (11); the driving end of the hollow rotating inner core tube (6) passes through the coaxial mechanical seal (12) and is connected to the active drive and speed control system via a coupling.

6. The evacuated tube solar collector according to claim 1, wherein, The active drive and speed control system includes a variable frequency geared motor, a temperature sensor, a direct radiation meter, a controller, and a frequency converter; The variable frequency reduction motor is connected to the drive end of the hollow rotating inner core tube (6) via a coupling, and is used to drive the hollow rotating inner core tube (6) to rotate; the temperature sensor is evenly arranged along the outer wall of the metal heat-absorbing inner tube (3) to detect the circumferential temperature difference of the metal heat-absorbing inner tube (3); the direct radiation meter is used to detect the solar radiation intensity. The controller is connected to the temperature sensor, the direct radiation meter and the frequency converter respectively, and the frequency converter is electrically connected to the variable frequency geared motor. The controller adjusts the speed of the variable frequency reduction motor through the frequency converter according to the solar radiation intensity and the circumferential temperature difference, so as to drive the hollow rotating inner core tube (6) to rotate.

7. The evacuated tube solar collector according to claim 6, wherein the inner core is rotatable. The temperature sensors are Pt100 temperature sensors, and there are four of them. Four Pt100 temperature sensors are evenly arranged circumferentially along the outer wall of the metal heat-absorbing inner tube (3), with an included angle of 90° between adjacent sensors. They are used to detect the circumferential temperature difference of the metal heat-absorbing inner tube (3) and transmit it to the controller.

8. The evacuated tube solar collector according to claim 6, wherein the inner core is rotatable. The controller has a built-in speed closed-loop control module. The speed closed-loop control module uses the speed determined based on solar radiation intensity as the reference speed and performs proportional-integral regulation based on the circumferential temperature difference to correct the speed of the hollow rotating inner core tube (6). When the circumferential temperature difference exceeds the preset temperature difference dead zone, the controller increases the speed of the variable frequency reduction motor according to the proportional-integral law. When the circumferential temperature difference falls back to within the preset temperature difference dead zone, the controller controls the speed of the variable frequency reduction motor to maintain or restore to the reference speed so as to drive the hollow rotating inner core tube (6) to rotate at the target speed.

9. The evacuated tubular solar collector with a rotating inner core according to claim 1, characterized in that, The outer radius of the hollow rotating inner core tube (6) is 1 / 2 of the inner radius of the metal heat-absorbing inner tube (3).

10. The evacuated tubular solar collector with a rotating inner core according to claim 1, characterized in that, When the hollow rotating inner tube (6) rotates, Taylor-Couette-Poiseuille flow is formed in the annular flow channel (5). Through radial mixing of the fluid and circumferential heat transport, the circumferential temperature difference of the metal heat-absorbing inner tube (3) is reduced and the thermal stress is decreased.

Images